Pipe string device for conveying a fluid from a well head to a vessel

ABSTRACT

A device including a pipe string device anchored to a sea floor. The device is configured to convey a fluid from a well head to a vessel during a drilling phase of a well. The fluid is located in the pipe string and needing, for well-technical reasons, to be given a flow boost. The pipe string that is anchored on the sea floor is provided with at least one injection point for a driving fluid.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage entry application of PCT/NO2007/000269, filed on Jul. 13, 2007, which claims priority to Norwegian Patent Application No. 20063269, filed in Norway on Jul. 14, 2006, the contents of these applications being incorporated herein by reference in their entirety.

BACKGROUND

The present inventor has recognized that, during the drilling for and the recovery of petroleum, it is often necessary to use a well fluid which is adapted for the conditions in the well with respect to, by way of example only and not by way of limitation, density and viscosity, among other things. It is common, for example, to use drilling fluid having a density of approximately 1.6 kg/l.

The present inventor has recognised that during the first phase of the drilling process, “disposable drilling fluid” is sometimes utilized, and the effluent cuttings are sometimes deposited on the sea floor, which the inventor has recognized may have a deleterious effect on the environment and also may result in increased costs.

U.S. Pat. No. 6,745,851 discloses a pump-operated solution which can recover and recirculate drilling fluid.

The present inventor has recognised that during drilling at great depths offshore, the head from the drilling vessel down to the well formation may become so great that drilling fluid penetrates into the formation. Such a flow of drilling fluid into the formation is sometimes undesirable because, for example, relatively expensive drilling fluid is lost, and because an inflow of this kind may reduce the future productivity of a well.

A method which is sometimes utilized in offshore wells involves pumping drilling fluid, as it is returning from the borehole, out at the well head on the sea floor, then flowing it back to the vessel via a separate pipe.

In this way, the static pressure in the borehole can be controlled, for example, by controlling the liquid head in the riser, if such is installed, between the well head and vessel.

NO Patent 319213 (WO2005052307) discloses a method directed towards controlling the liquid pressure in the well by filling the upper portion of the riser with a fluid having a different density relative to the density of the drilling fluid.

The present inventor has recognised that at relatively great sea depths, at which the return pipe necessarily is long, the necessary pump pressure at the sea floor is relatively high because of the density and viscosity of the drilling fluid. It is difficult to achieve the necessary flow rate without having to use pipes of a relatively large diameter, which entails increased pipe weight and thereby considerably higher investment costs.

SUMMARY

The present invention relates to a pipe string. More particularly, it relates to a pipe string for conveying a fluid from a well head to a vessel, in which, for technical reasons, the fluid located in the pipe string is to be given a flow boost, and in which the pipe string is provided along its length with at least one injection point for a driving fluid. The injection point may be formed by a fluid-operated ejector. The invention also includes a method of using the device.

In an exemplary embodiment, there is a pipe string for conveying a fluid from a well head to a vessel, in which the fluid located in the pipe string is to be given a flow boost, wherein the pipe string is provided along its length with at least one injection point for a driving fluid.

In some embodiments, the injection point may comprise a fluid-operated ejector.

One or more such injection points can be disposed at suitable intervals along the pipe string from the sea floor and up to the vessel. The pipe string forms a separate flow path relative to a possible riser, in some embodiments.

In an exemplary embodiment, where the injection point comprises an ejector, a possible ejector located above will relieve the ejector located below, so that this ejector starts a flow feeding the ejector located above with fluid.

Alternatively, in another exemplary embodiment, a pump may be arranged which pumps the fluid through the pipe string, wherein one or more ejectors at the upper portion of the pipe string form auxiliary apparatuses for a sufficient flow rate through the pipe string to be achieved.

In some embodiments, the driving fluid has a lower density than the fluid located in the pipe string. Thus, on injection of a second fluid, the overall liquid pressure within the fluid string at the sea floor will be reduced.

If the second fluid comprises a gas, the gas may expand as it rises in the pipe string, thereby further reducing the overall liquid pressure within the pipe string at the sea floor.

In some embodiments, the pipe string may be anchored on the sea floor and be provided with buoyancy bodies at its upper portion, and/or may be suspended from the vessel which then carries the weight of the pipe string.

The device and method according to the invention may provide a satisfactory flow rate in the pipe string, even with the use of a pipe string of a relatively small diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically presents a vessel which is provided with a pipe string in accordance with an exemplary embodiment of the invention.

FIG. 2 schematically presents the invention in an alternative embodiment.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The following describes some exemplary embodiments, including apparatuses and methods, of the present invention.

Referring to FIG. 1, a pipe string 1 which is connected at its lower end portion to a well head 2 on the sea floor 4, and which is connected at its upper end portion to a separator 6. The separator 6 is located on a vessel 8.

The vessel 8 is typically working a well 10, which is in the ground, and is connected to the well 10 by a pipe connection 12 extending through the well head 2. Dependent on the operations involved, the pipe connection 12 may comprise, in a manner known per se, one or more of drill pipe, marine riser, work riser or other well-intervention tools.

The pipe string 1 is anchored on the sea floor 4 by an anchor 14. At its upper portion, near the sea surface 16, is arranged a buoyancy body 18 which is arranged to take the weight of the pipe string 1.

The pipe string 1 is provided with fluid-operated ejectors 20 suitably spaced apart, which are supplied with driving fluid from the vessel 8 via at least one driving-fluid pipe 22.

When a fluid is to flow through the pipe string 1 from the well head 2, the pressurized fluid supply via the driving-fluid pipe 22 from the vessel 8 to the ejectors 20 is opened. The flow is started by each ejector 20 supplying the necessary pressure to the fluid until the fluid flows to the next ejector along the pipe string 1.

At the vessel 8, the fluid enters the separator 6, in which driving gases that may be present are separated from the rest of the fluid before the remaining fluid flows on for treatment in, for example, screening machines, not shown.

The return pressure at the well head 2 can be controlled by adjusting the driving-fluid pressure into the ejectors 20.

In an alternative embodiment, as may be seen in FIG. 2, a mechanical pump 24 is arranged at the lower portion of the pipe string 1. The ejectors 20, which are arranged at the upper portion of the pipe 1, are used to increase the flow rate through the pipe string 1 beyond that effected by the pump 24 on its own.

Given the disclosure of the present invention, one versed in the art would appreciate that there are other embodiments and modifications within the scope and spirit of the present invention. Accordingly, all modifications attainable by one versed in the art from the present disclosure within the scope and spirit of the present invention are to be included as further embodiments of the present invention. 

1. A device comprising a pipe string anchored to a sea floor and adapted to convey a fluid from a well head to a vessel during a drilling phase of a well, the fluid being located in the pipe string and needing, for well-technical reasons, to be given a flow boost, wherein the pipe string that is anchored on the sea floor is provided with at least one injection point for a driving fluid.
 2. The device in accordance with claim 1, wherein the at least one injection point comprises a fluid-operated ejector.
 3. The device in accordance with claim 1, wherein a mechanically working pump is connected to the pipe string.
 4. The device in accordance with claim 1, wherein the pipe string leads into a separator tank on the vessel.
 5. The device in accordance with claim 1, wherein the pipe string is anchored on the sea floor by an anchor and provided with a buoyancy body near a sea surface.
 6. The device in accordance with claim 1, wherein the pipe string is suspended from the vessel and connected to the well head by a flexible connection.
 7. A method comprising providing flow assistance to a fluid located in a pipe string during a drilling phase of a well, the fluid being conveyed by the pipe string from a well head to a vessel, wherein the method further comprises supplying the pipe string with a driving fluid that has a lower density than the conveyed fluid at at least one injection point located on the pipe string.
 8. The method in accordance with claim 7, further comprising supplying, at the at least one injection point, a driving fluid which has a lower specific gravity than the fluid being conveyed by the pipe string.
 9. A device comprising a pipe string assembly, wherein at least a substantial portion of the pipe string assembly is interposed in a sea between a sea floor and a surface of the sea, wherein the pipe string assembly includes at least one fluid ejector adapted to inject a driving fluid into the pipe string assembly to give a fluid contained in the pipe string assembly a flow boost to assist the fluid in the pipe string assembly to flow away from the sea floor towards the surface of the sea.
 10. The device of claim 9, wherein the pipe string assembly includes a plurality of fluid ejectors spaced along the pipe string assembly.
 11. The device of claim 9, wherein the pipe string assembly includes at least five fluid ejectors spaced along the pipe string assembly.
 12. The device of claim 9, wherein the pipe string assembly includes at least five fluid ejectors spaced along the pipe string assembly substantially spaced along the pipe string assembly in even intervals.
 13. The device of claim 9, wherein the pipe string assembly includes a plurality of fluid ejectors spaced along the pipe string assembly, wherein a lower fluid ejector, relative to a higher fluid ejector in a direction opposite the direction of gravity, is adapted to inject driving fluid into the pipe string assembly to supply a pressure to the fluid in the pipe string assembly to drive the fluid in the pipe string assembly to the higher fluid ejector.
 14. The device of claim 9, wherein the pipe string assembly extends from a location proximate a well head on the sea floor to a location proximate a buoyant vessel located on the surface of the sea, wherein a separator is located on the buoyant vessel, and wherein the separator is adapted to separate driving fluid from a drilling fluid in the pipe string assembly.
 15. The device of claim 9, wherein the device is adapted to control a return pressure at a well head located proximate the sea floor to which the pipe string assembly is connected.
 16. The device of claim 9, wherein the device is adapted to control a return pressure at a well head located proximate the sea floor to which the pipe string assembly is connected by adjusting a driving-fluid pressure of one or more of the at least one fluid ejector.
 17. The device of claim 9, wherein the device further comprises a mechanical pump in fluid communication with the pipe string assembly at a location proximate the sea floor, wherein the mechanical pump is adapted to increase a flow rate of fluid in the pipe string assembly.
 18. A method, comprising: obtaining the device according to claim 9, directing a drilling fluid in the direction of gravity from a location proximate the surface of the sea to a well head proximate the sea floor; directing the drilling fluid directed to the well head to the pipe string assembly; directing a driving fluid to one or more of the at least one fluid injector; and driving the drilling fluid directed to the pipe string assembly in a direction away from the direction of gravity by injecting the driving fluid through one or more of the at least one fluid injector.
 19. The method of claim 18, wherein the pipe string assembly extends from the well head to a buoyant vessel located proximate the surface of the sea.
 20. The method of claim 18, wherein the pipe string assembly includes a plurality of fluid ejectors spaced along the pipe string assembly, wherein a lower fluid ejector is located lower than a higher fluid ejector located higher than the lower fluid ejector in a direction opposite the direction of gravity, the method further comprising injecting the driving fluid into the pipe string assembly using the lower fluid ejector to supply a pressure to the fluid in the pipe string assembly to drive the drilling fluid in the pipe string assembly to the higher fluid ejector. 